Twitter in a nutshell

One of those questions that doesn't seem to go away is this: "What is Twitter, and why should I care?"
While it's certainly not necessary to care, you certainly can't be blamed for wondering what it's all about. Here's a very basic primer:
Twitter is like a conversation in a busy bar. Inside this bar are some of your friends and many strangers. This bar is completely open to the public and has limitless capacity.
Inside this bar, just like inside any other, some people sit quietly by themselves, some listen in on the conversations around them, and some are talking. A few talk a whole lot.

Posting something on Twitter (most people now call a post a "tweet") is like saying something inside the bar. As with most bars, there's a lot of background noise, so you're only able to get out snippets of conversation. Twitter arbitrarily limits each comment to 140 characters, but as with anything else, the art is in the constraints.

Most individual tweets are along the lines of one of these themes:

"Hey, this is interesting:"

"Are you watching this thing on TV right now?"

Quips and attempts at humor

Shameless plugs for attention

Many of these posts begin with (or include) a user's name, starting with the @ symbol (as in @briangongol). A post including an @username is like saying "Hey, you!" It is specifically intended to get the attention of an individual user, though everyone else can listen in. (And, conversely, the individual whose attention you're trying to get is free to ignore you...though they usually will at least be alerted to your comment.)

A hashtag (like #winter or #justkidding) is the equivalent of either (a) what you'd say to explain your conversation to an unrelated party who just listened in (as in, "We're talking about ___"), or (b) what you'd say under your breath to get someone to laugh.

Users on Twitter have the option to follow other people and to be followed. A small and dwindling number of people attempt to "protect" their tweets by hiding them from the public and sharing them only with pre-approved followers, but that tends to defeat the purpose of speaking up (either on Twitter or in a bar), and doesn't really offer much security, since anyone can repeat what you just said or tweeted.

You can see these lists for any user on Twitter:

Following: Who you're listening to

Followers: Who's listening to you

There are also options to create lists. Lists are a way to selectively sample what people are saying when they're likely to be talking about similar things. There are lists of all types on Twitter, like essential reading and people in Iowa. Users can create and manage their own lists, as well as subscribing to lists belonging to others.

What makes Twitter attractive?

People on TV (and other celebrities) can talk back to you. William Shatner does a lot of this.

You can share opinions openly and without having to pass through any gatekeepers. Cory Booker leveraged this direct engagement extremely well as a mayor.

Most news services and media outlets have figured out that they need to constantly feed their latest material into Twitter. It can be an absolute non-stop firehose of news, if you let it. But its immediacy can't be beaten.